1. Field of the Invention
This invention relates to novel xanthene compounds and to their use, e.g., as light-screening dyes in photographic products and processes.
2. Description of the Prior Art
It is well known that photographic film, and especially multicolor films, may and generally do vary from lot to lot, notwithstanding efforts to "repeat" previous films. Manufacturers of multicolor photographic films have developed a number of procedures to minimize the effects upon the final multicolor image of unavoidable variations in the manufacturing operations. These variations are reflected primarily in shifts in color balance as reflected in mismatching of the D log E curves of the individual red, green and blue exposures. Equipment used to coat multicolor films is highly precise but variations between intended coverage of silver halide and/or the dye image-forming materials do occur. Repeat batches of silver halide emulsions may, and usually do, vary in their photographic response. Individual layers may be dried to slightly different degrees. Films are stored for a period of time after coating to allow the films to "age", so that changes in sensitometry following coating have an opportunity to reach a plateau prior to sale. If the film is designed to be developed by a photofinisher or in a darkroom, processing of the exposed multicolor film is controlled within very narrow limits, typically within plus or minus a half degree of prescribed temperature, in order to minimize sensitometric variations from film to film. Where the multicolor film is of the negative type, an opportunity to adjust the sensitometry occurs in printing the desired final positive image, during which operation the printing exposure may be appropriately color filtered.
The basic sources of sensitometric variations noted above exist also in multicolor diffusion transfer films, with the added complication that once the film is shipped, the sensitometric properties are essentially fixed. The opportunity for adjustment provided in darkroom processing, practically speaking, is unavailable for users of self-developing films. While professional and advanced amateur photographers may be skillful enough to utilize color correction filters to at least partially "rebalance" the color balance, ordinary users of the film would only be confused by such additional operations.
It is well known to use light-screening dyes in photographic elements. Such a dye may be incorporated as a filter dye in a light-sensitive emulsion layer(s) or in a layer coated over one or more light-sensitive emulsion layers or between two differently color-sensitized emulsion layers to modify the light record in the emulsion layer or to control the spectral composition of light falling on the underlying light-sensitive layer, or it may be incorporated as an antihalation dye in a non-light-sensitive layer positioned on either side of a support carrying the light-sensitive layer(s).
The dyes employed for these purposes, in addition to having the requisite spectral absorption characteristics for their intended use, should be photochemically inert, that is, they should not have any adverse effect on the properties of the light-sensitive emulsion layer(s), and also, they should be capable of being decolorized or removed during photographic processing so as not to leave stain in the processed photographic element. In photographic processes where the dye is removed by being dissolved in a processing solution, it is usually preferred that the dye also decolorize in order to avoid contamination of the processing solution and to prevent staining from residual dye in the processed light-sensitive element.
Though various classes of dyes have been proposed for use in antihalation and color correction filter layers, the dyes heretofore employed have not been altogether satisfactory. Some of the dyes tend to reduce sensitivity, fog or exert other adverse effect on the light-sensitive material. However, the major drawback of previously employed dyes is their tendency to cause stain due to incomplete decolorization or reversal of some of the decolorized form to the original colored form. For example, some classes of dyes rely on the presence of a reagent, such as, a sulfite for "bleaching", i.e., decolorization and unless the dyes are removed from the light-sensitive material during or after processing, their color may reappear in time.
Among the classes of light-screening dyes used previously are the triarylmethanes and xanthenes. For example, U.S. Pat. Nos. 1,879,537; 1,994,876; 2,350,090 and 3,005,711 disclose the use of fuchsone-type dyes in antihalation layers, and U.S. Pat. Nos. 3,406,069 and 3,615,548 are concerned with the metal chelates of fuchsone dyes as antihalation dyes. These and other types of triarylmethane dyes suffer from one or more of the drawbacks discussed above, and in particular, prior dyes of this type have been difficult to keep decolorized at the pH's normally encountered during processing subsequent to "bleaching" and in the final product. Xanthenes have been employed in antihalation layers that are removed during photographic processing. For example, U.S. Pat. Nos. 2,182,794; 2,203,767 and 2,203,768 disclose the use of rhodamine dyes in certain antihalation layers that are removed during processing in an acid bath or a plain water rinse bath depending upon the solubility characteristics of the particular layer.
Aforementioned U.S. patent application Ser. No. 106,938 is directed to photographic products and processes employing light-screening dyes of the formula ##STR2## R' is alkyl; Y is an electron-withdrawing group and n is 0 or 1. These compounds are colored, i.e., capable of absorbing visible radiation, and at an alkaline pH, are converted to a colorless product by undergoing an irreversible cleavage reaction with base. The colorless product formed is a new compound which is different from and non-reversible to the colored compound by a change in pH. In particular, it is the X group substituted on the phenyl moiety that undergoes the irreversible cleavage reaction in alkaline solution that is complete within a predetermined time at a predetermined alkaline pH to give the new colorless compound, namely, the cyclic sulfonamide, ##STR3## wherein R' and n have the same meaning given above. These compounds offer advantages over the light-screening dyes previously used because of their ability to decolorize completely and irreversibly to a substantially inert colorless product.
As discussed in said application, the compounds of formula A may be prepared
(a) by reacting sulfonefluorescein dichloride with indoline to give the di(indolinyl)-substituted compound of the formula ##STR4##
(b) reacting said di(indolinyl)-substituted compound with phosphorous pentachloride or thionyl chloride to give the corresponding sulfonyl chloride of the formula ##STR5##
(c) reacting said sulfonyl chloride with ammonia to give the corresponding cyclic sulfonamide of the formula ##STR6##
(d) reacting said cyclic sulfonamide with an alkylating agent to give the corresponding N--R' sulfonamide of the formula ##STR7##
(e) reacting said N--R' sulfonamide with a reducing agent to give the corresponding reduction product of the formula ##STR8##
(f) reacting said reduction product with the appropriate acylating agent, for example, ClCOCH.sub.3 or ClCO.sub.2 (CH.sub.2).sub.2 Y to give the leuco dye precursor of the formula ##STR9## R' is alkyl and Y is an electron-withdrawing group;
(g) reacting the compound of step (f) with chlorosulfonic acid in a solvent, such as, methylene chloride to give mainly the monosulfonated product or in a more polar solvent, such as, acetic anhydride to give essentially the disulfonated product of the formula ##STR10## wherein n is 0 or 1 and X has the same meaning given above; and
(h) oxidizing said leuco dye precursor preferably using o-chloranil as the oxidizing agent followed by isolating the dye product from its o-chloranil complex with an acid to yield the dye product. Optionally, the compound of step (a) also may be synthesized in a stepwise fashion by replacing only one of the chloro groups of the starting sulfonefluorescein dichloride with an indolinyl group and then reacting this intermediate with indoline to replace the remaining chloro group.
The present invention is directed to certain sulfonated xanthene compounds, namely, the compounds of formula B above. In addition to being the cleavage products of the light-screening dyes described above, they also have been found useful as light-screening dyes per se.